[Tutor] Sorting a list in ascending order [RESOLVED]

[Ken G.]

On 04/29/2016 05:10 PM, Martin A. Brown wrote:
> Greetings Ken and welcome to Python,
>
>> Using Linux 2.7.6 in Ubuntu 14.04.4. Thanks.
> Thank you for this information.  I have one tip for you:  While
> Python 2.x will still be around for a while, if you are learning
> Python today, I'd suggest Python 3.x. You can read more about the
> differences online (or ask here), if you care.  The only syntax
> difference that usually trips up beginners is the following:
>
>    print line     # Python 2.x
>    print(line)    # Python 3.x
>
> Though there are other differences, this is one of the most obvious
> to all Python programmers.  With that said, I'll just answer your
> question using Python 2.x, since everything else in your example
> will work perfectly the same in either version.
>
> I intend to suggest what you should read, and then what you should
> try to run in order to address your question(s).
>
> I will paste my entire interactive Python sessions below.  Did you
> know that you can use the Python interpreter as a shell to test out
> how things behave?  Very handy.  Try typing 'python' at the CLI and
> you should see this:
>
>    $ python
>    Python 2.7.8 (default, Sep 30 2014, 15:34:38) [GCC] on linux2
>    Type "help", "copyright", "credits" or "license" for more information.
>    >>>
>
> So, when you see ">>>" below, that's in the Python shell (2.7.8 in
> my case, 2.7.6 in yours).
>
>> In entering five random number, how can I best sort it into
>> ascending order, such as 0511414453?
> OK, so you have five random numbers, but you seem to want to print
> them without any visual space between them.  A bit strange, but OK!
>
> Fragment #1:
>
>> number01 = "41"
>> number02 = "11"
>> number03 = "05"
>> number04 = "53"
>> number05 = "44"
> Observation:  You define a variable called 'number01', which
> actually contains a string value.  You can call the variable
> anything you want, but that will not change the type of the object
> to which your variable name is bound.  For example:
>
>    >>> number01 = "41"
>    >>> type(number01)
>    <type 'str'>
>
> Suggestion #1, try this instead:
>
>    >>> number01 = 41
>    >>> type(number01)
>    <type 'int'>
>
> Ah-ha!  Now, we are dealing with integers (numbers).
>
> Fragment #2:
>
>> line = number01 + number02 + number03 + number04 + number05
> Observation:  Since all of the variables (named number01, number02,
> number03, etc....) contain strings, you are using string
> concatenation to create a new string.  After the above command
> executes, you have this:
>
>    >>> line
>    '4111055344'
>    >>> type(line)
>    <type 'str'>
>
> Comment:  You don't really want a string, do you?  Keep reading for
> a moment, and I'll come back to this.
>
> Also, I don't think you really want to add the integers.  That would
> be 41 + 11 + 05 + 53 + 44 = 154.  But, you want to keep the numbers
> and sort them.  We will need to keep them in a list.  And, Python
> has a data structure for you...called, obviously enough list().
>
> Fragment #3:
>
>> print
>> print line
>> line.sort()
>>
>> Traceback (most recent call last):
>>   File "Mega_Millions_01_Tickets_Entry_TEST_TEST.py", line 11, in <module>
>>     print line.sort()
>>
>> AttributeError: 'str' object has no attribute 'sort'
> Observation:  This message is called an Exception, in Python.
> There are many different kinds of exceptions--this one is called
> AttributeError, but the message of the exception is the important
> part for us here.  It doesn't make sense to sort a string.  You can
> sort two strings, of course.  But not a single string.
>
> Anyway, the important thing about the Exception is it tries to give
> you a good deal of information about which line of code did
> something that was problematic, and what code called that code (this
> is why it's called a "Traceback").
>
> Now, I'll rewind to the beginning and try to go through the problem
> again, changing a few pieces of your program to get you closer to
> your solution.
>
> First, let's use the right datatype, an int, for each number.
> Second, let's use a list() to store the numbers (instead of five
>    separate named variables; easy to mistype names).
> Third, let's sort it.
> Then, let's print it.
>
>    >>> nums = [41, 11, 5, 53, 44]  # -- create/populate a list
>    >>> nums
>    [41, 11, 5, 53, 44]             # -- still looks good
>    >>> nums.sort()                 # -- sort, in place!
>    >>> nums
>    [5, 11, 41, 44, 53]             # -- Ta-da!
>
> I'm going to do the same thing a slightly different way, now, so you
> can see how to add stuff to a list:
>
>    >>> nums = list()
>    >>> nums.append(41)
>    >>> nums.append(11)
>    >>> nums.append(5)
>    >>> nums.append(53)
>    >>> nums.append(44)
>    >>> nums
>    [41, 11, 5, 53, 44]
>
> In each case the variable 'nums' still contains the same data.  We
> just got there in a different series of steps.  You may decide which
> makes more sense to you in any given situation.
>
> So, suggestion, play with lists, and see how they work.
>
> Now, we have to figure out how to print the contents of the list.
> Here's one way, but it is not the output you appear to want.
>
>    >>> print nums
>    [5, 11, 41, 44, 53]
>
> I'm guessing you want '05 11 41 44 53'.
>
> There are many ways to convert from one data type to another or to
> format the output of something when you want to print it.  So, I
> will show you one or two ways, but there are many ways you could do
> this.  It's good to learn to read them all, but you can always pick
> the one that works best for your situation.
>
> Conversion is one way The 'str' function converts the int (17) into
> a string.  I store that in a variable called string_num.  The 'type'
> function tells us that the contents of the variable string_num are
> of type 'str':
>
>    >>> num = 17
>    >>> string_num = str(num)
>    >>> string_num
>    '17'
>    >>> type(string_num)
>    <type 'str'>
>
> This is useful, but, we are not going to do that here.
>
> Detour to format strings!  What I'm about to show is how you can
> format a value (usually in preparation for output/printing).
>
> There are many different ways to print numbers, as you may know from
> prior mathematics classes.  (Ignoring some possibly important
> subtleties for a moment,) 1, 1.0, 1e0 are different ways of printing
> the value of 1.
>
>    >>> num = 7
>    >>> '%d' % (num,)
>    '7'
>
> Let's add a leading zero:
>
>    >>> '%02d' % (num,)
>    '07'
>
> I think that's what you want.
>
> Returning to your data, you might be worried about that 5, which was
> missing its leading zero.  Well, as you can see the number is never
> stored with that leading zero.  A number is a number.  However, we
> can produce the leading zero when we print.
>
>    >>> stringified_nums = list()
>    >>> for x in nums:
>    ...     stringified_nums.append('%02d' % (x,))
>    >>> stringified_nums
>    ['05', '11', '41', '44', '53']
>
> Lastly, let's print the stringified_nums; do you want to print them
> with colons separating the numbers, semicolons, commas, a hyphen?
>
>    >>> ':'.join(stringified_nums)
>    '05:11:41:44:53'
>    >>> ','.join(stringified_nums)
>    '05,11,41,44,53'
>
> Now, I'm going to put it all together.....
>
>    nums = [41, 11, 5, 53, 44]
>    nums.sort()
>    outstr = list()
>    for x in nums:
>        outstr.append('%02d' % (x,))
>    print ' '.join(outstr)
>
> Hopefully that made sense to you.  I include a few links to various
> places in the Python project documentation that may help you.  In
> particular, I'd recommend that you read through the Python tutorial
> and keep a Python interactive interpreter open while you do that, so
> you can play with the different datatypes and functions.
>
> If you have more questions, please ask here, there are quite a few
> others who are happy to help.
>
> Best of luck,
>
> -Martin
>
> Tutorial:      https://docs.python.org/2/tutorial/introduction.html
>   on numbers:   https://docs.python.org/2/tutorial/introduction.html#numbers
>   on strings:   https://docs.python.org/2/tutorial/introduction.html#strings
>   on lists:     https://docs.python.org/2/tutorial/introduction.html#lists
>
> Reference:     https://docs.python.org/2/library/index.html
>   on datatypes: https://docs.python.org/2/library/stdtypes.html#numeric-types-int-float-long-complex
>   on sequences: https://docs.python.org/2/library/stdtypes.html#sequence-types-str-unicode-list-tuple-bytearray-buffer-xrange
>   on functions: https://docs.python.org/2/library/functions.html
>
>    (A list is a sequence.  There are other types of sequences, but
>    the section on sequences, should give you some idea of how to play
>    with lists.)
>
Martin: I have been using Python2 for several years now and I have yet 
been able to change over to Python3. I am not together sure if Python3 
is now more stable to use and more commonly use. If so, I will gradually 
change over but do realize there is a learning curve to learn. It will 
be slowly done but sooner or later, I will be using Python3. I wonder if 
there is a script to translate my Python2 programs to Python3 format. 
Hmm. I will some searching for such an animal. Hey, thanks for your 
encouragement. Much appreciated.

Ken